EFFECTS OF ROTTLERIN, AN INHIBITOR OF CALMODULIN-DEPENDENT PROTEIN-KINASE-III, ON CELLULAR PROLIFERATION, VIABILITY, AND CELL-CYCLE DISTRIBUTION IN MALIGNANT GLIOMA-CELLS

Calmodulin-dependent protein kinases phosphorylate certain substrates that have been implicated in regulating cellular proliferation, For ex ample, upon mitogenic stimulation, there is a rapid activation of calm odulin-dependent protein kinase III (CaM kinase III), which leads to t he phosphorylation of elongation factor 2. Recently, our laboratory de monstrated that the activity of CaM kinase III is increased in glioma cells following exposure to mitogens and is diminished or absent in no nproliferating glial tissue, Rottlerin, a hydroxy-2,2-dimethyl-6-(2,4, 6-trihydroxy-3-methyl- 5-acetylbenzyl)-8-cinnamoyl-1,2-chromene isolat ed from the pericarps of Mallotus phillippinensis, has been shown to b e an effective CaM kinase III inhibitor. Therefore, we evaluated the e ffects of rottlerin on the growth and viability of glioblastoma cell l ines, Rottlerin decreased growth and induced cytotoxicity in rat (C6) and two human gliomas (T98G and U138MG) at concentrations that inhibit ed the activity of CaM kinase III in vitro and in vivo. Far less demon strable effects were observed on other Ca2++/CaM-sensitive kinases, In cubation of glial cells with rottlerin produced a block at the G(1)-S interface and the appearance of a population of cells with a <2N compl ement of DNA, In addition, rottlerin induced changes in cellular morph ology such as cell shrinkage, accumulation of cytoplasmic vacuoles, an d packaging of cellular components within membranes, These data sugges t that CaM kinase III may be an important link between the activation of CaM-dependent signaling, proliferation, and viability in malignant cells, and that inhibition of CaM kinase III may represent an interest ing pharmacological target in malignant gliomas.